Presently, the change of the dark-and-light status of each segment of an EL independently is controlled by a corresponding transistor, that is to say, the number of transistors increases in proportion to that of the EL. Therefore, in a multiple segment EL, a large number of transistors are required to control the dark-and-light status of the EL, which may increase the area of the circuit board for controlling the EL, and make the design of a circuit board complex and the cost higher. In addition, displaying an EL with different dark-and-light scale is generally controlled by increasing or decreasing the input voltage of a power supply circuit of the EL, or by controlling the frequency of an oscillating circuit in the power supply circuit of the EL. Accordingly, the driving circuit board should comprise the power supply circuit, which further increases the area of the circuit board. On the other hand, it is inconvenient for the user to have to be familiar with the driving method of an EL and the design procedures of a power supply circuit, in order to achieve a proper design of a driving circuit board of an EL.